Safety fuse



Dec. 14, 1937. D. E. PEARSALL SAFETY FUSE Filed Oct. 16, 1956 INVENTOR TT R EYS Patented Dec. 14, 1937 UN] STATES PATENT OFFICE ssrnrr FUSE I Application October 16, 1936, Serial No. 105,857

8 Claims.

My present invention relates to fuses for igniting explosives, fireworks and the like, and more particularly to safety fuse for blasting; and aims to provide certain improvements therein.

In the-various commercial brands of safety fuse for blasting which are now obtainable, the powder core is directly surrounded or enclosed in a covering of combustible material such as cellulosic yarns, textiles, paper and the like, and

this core is then waterproofed and built up to size by the successive applications of various combustible covering material and filler compounds. When the fuse is ignited the powder burns and carries the fire to the blasting cap at a definite and predetermined rate. The burning of the powder creates temperatures ranging from 1000" F. to 1800 F. and hence causes more or less charring and burning of other structural materialsof the fuse which are composed of combusa0 tible material. This burning and charring has numerous objections, viz., (1) it produces smoke and gases, 55% of which in many brands of safety fuse is directly traceable to the combustible ma= terials other than the powder; (2) such smoke Ii and gases may influence the burning mechanism if the fuse is too tightly confined in the bore hole; (3) an excess of smoke and gas is undesirable for underground work as it reduces visibility and creates discomfort; (4) the burning and char- 80 ring throws the powder ofi balance" and maythus cause fluctuations in the burning mechanism; and (5) after chan'ing, the used fuse carcass may continue to smoulder and constitute a potential fire hazard, especially where used,

85 in contact withinfiammable material, for example, in forest service blasting after an ex.- tremely dry period.

Numerous attempts have been made to elimi-- nate these objectionable characteristics by vary- 40 ing both the structure and the material used in the fuse construction. For example, it hasrbeen previously proposed to substitute asbestos yarns and asbestos paper or cloth tapes for the cellulosic materialnow employed. These asbestos materials, however, have not proved satisfactory because the asbestos fiber is relatively short and smooth and it is necessary to add cotton fiber (sometimes as much as to it in order to give it sufllcient strength for the commercial production of yarns and fabrics. Further, the asbestos yarns, papers, and-cloths usually contain combustible adhesives along with the combustible cotton, so that when burned they actually do produce a fairly large amount of gas 55 and smoke. i

Another attempt toward overcoming the objections previously recited has been to impregnate the combustible yarns, etc., with so-called fireproofing materials. Actually, however, such materials do not fireproof the combustibles but only 5 render them more fire-resistant, i. e., they usually lower the charring temperature of the yarns,- etc., so that combustion takes place without flame and is not rapidly communicated. Hence the so-called fireproofed materials actually do burn l0 and produce appreciable amounts of gas and smoke. -Moreover, to secure uniform results with such fireproofed materials, the impregnation must take place while the yarn is in the skein form, thus rendering the process uneconomical.

The present invention contemplates overcoming the various objections hereinbefore enumerated by producing a safety fuse wherein the combustible powder core is enveloped in. a sheath of non-combustible fused mineral matter, more spe- 20 cifically, by enveloping the powder core in a. sheath formed of glass fiber yarns. Preferably these yarns are substituted for the combustible cellulosic spinning yarns now conventionally used to envelop the powder core, although the center thread through the powder core and even other elements of the fuse may likewise be made of such non-combustible material. In this connection applicantihas found by experiment that a fuse with a powder core envelope of glass fiber spinning yarns when burned reduces the total volume of smoke and gas formed by about 40%, while fireprooflng of the combustible yarns reduces the volume by only about 14%. The greatest possible reduction in volume of generated smoke and gas obtainable by burning safety fuse is that which results by burning the powder per 'se in a non-combustible material, such as lead tubing. When this is done the total volume of smoke and gas formed is reduced by about 54%. 'There- 40 fore the reduction in gas and smoke obtained by the use of glass fiber yarn is equal to 40 divided by 54, or about 74% of that theoretically possible. I

The invention inits practical application to the manufacture of safety fuse and the like primarily resides in substituting for the jute spinning threads which encase the powder core, glass fiber yarns, threads, tape or cloth formed from such yarns. Hence in describing my invention I have illustrated the same in the accompanying drawing as applied to a standard type safety fuse.

Referring to the drawing, let the reference character l0 indicate a powder core which .sur-

rounds a central longitudinal strand or strands l I, the powder core in turn'being surrounded by a casing l2. The powder core Ill and the'casing l2 may be considered as the fuse core. Surrounding the fuse core or casing [2 are one or more plastic coatings of waterproof material l3, such as asphaltum, gutta percha and the like, which serves to prevent moisture gaining access to the powder core and in building up the fuse to proper diameter. Enclosing the coating I3 is an envelope of material l4, such as paper and the like, which is held in contact with the coating l3 by countering strands l5 which are wound around the paper under sufficient tension to transfer through the medium of the paper a pressure on the underlying plastic coating I3, causing this to become embedded in the strands forming the casing l2. Surrounding the countering strands I5 is an outer casing or coating l6 preferably of waterproof material, such as wax and the like. The safety fuse thus far described may be considered as a standard type in use at the present time and its construction and method of formation are described in detail in United States Patent No. 1,023,142, dated April 16, 1912.

As before stated, my present invention resides in the particular character of the casing or envelope I! which encases or ensheathes the powder core. This casing, in its broadest aspect, consists of fused mineral matter. More specifically this fused mineral matter may be in the form of yarns produced from molten glass or from mineral wool fibers such as are made from blown rock or slag. These fibers may be either directly spun about the powder core as it is being formed, or they may first be woven, twisted or matted into a tape or cloth, which may subsequently be used to ensheathe the powder core. casing I2 is to be formed of fused mineral matter instead of cellulosic material as heretofore employed, it will be apparent that if desired, the center strand or strands II, as well asone or more of the'bullt up coating materials ll and l5, may likewise be formed wholly or in part of such fused mineral matter. 4

I have found that the substitution and use of glass" spinning yarns for the jute spinning yarns now conventionally employed reduces the objectionable carbqn monoxide present in the gas composition resulting from the burning of the fuse, from about 20% to 10%, i. e., a reduction of 50%.

While primarily the- The use of such glass fiber spinning yarns also results in a fuse structure which will not smoulder after the powder core has ceased burning. Moreover, since glass fiber yarns are not affected by moisture or water, they provide an envelope for the powder core which is more moisture proof and waterproof than an envelope composed of cellulosic fibers.

It will thus be recognized that I have provided a definite and distinct improvement in safety fuse which overcomes the various objectionable characteristics inherent in safety fuse as now constituted, and while I have described my invention as applicable to a particular type of safety fuse, it is to be understood that I do not wish to limit myself to the invention as illustrated, since in its broader aspect it contemplates either partial or complete elimination of cellulosic material from safety fuse. The invention, therefore, is to be construed in the spirit of the appended claims.

What I claim is:

1. A fuse for igniting explosives, fireworks and the like, comprising a powder train directly encased in iused mineral matter.

2. A fuse for igniting explosives, fireworks and the like, comprising a powder train directly encased in a sheath formed of yarns of fused mineral matter.

3. A fuse for igniting explosives, fireworks and the like, comprising a powder train directly encased in a sheath formed of glass fiber yarns.

4. A fuse for igniting explosives, fireworks and the like, comprising a powder train directly encased in a sheath composed of yarns of mineral wool fibers formed from blown rock or slag.

5. A safety fuse comprising a powder core directly enveloped in a sheath formed of fibers of fused mineral matter.

6. A safety fuse comprising a powder core directly enveloped in a sheath formed of fibers of fused mineral matter and a waterproof coating enclosing said sheath.

"1. A safety fuse comprising a powder core directly enveloped in a sheath formed of glass fiber yarns.

8. A safety fuse comprising a powder core directly enveloped in a sheath formed of glass fiber yarns and a layer of waterproof material enclosing said sheath.

DAVID E. PEARSALL. 

